1. Field of the Invention
The present invention relates to a laser projection device, for example, a scanning laser projection device (laser projector or the like) that deflects and scans laser light with a mirror to project an image onto a screen surface.
2. Description of Related Art
Various laser projection devices have been suggested (for example, see Patent Documents 1 and 2) which form a two-dimensional image by deflecting laser light in mutually orthogonal first and second scanning directions and then two-dimensionally scanning a surface to be scanned with a beam spot. For the deflection of laser light, a mirror, such as a polygon mirror, a galvanomirror, a MEMS (Micro Electro Mechanical Systems) mirror, or the like, is typically used. However, mirrors, such as the galvanomirror, the MEMS mirror, and the like, that are sinusoidally driven suffer from several problems. For example, these mirrors face the problem that the scanning speed on the surface to be scanned slows down at the periphery, which results in image quality deterioration due to nonuniformity in the amount of light. In addition, these mirrors face the problem that distortion occurs on the two-dimensional image formed on the surface to be scanned. Attempts to solve such problems lead to complication or upsizing of an optical system or increases loads imposed on an electrical circuit, etc.
A laser projection device described in Patent Document 3, in order to achieve both ensuring the constant-speed scanning performance and correction of projection distortion, uses optical surfaces of different shapes for directions horizontal to and vertical to laser light after deflected. A laser projection device described in Patent Document 4, in order to achieve downsizing of the device, makes laser light with different convergence performance in a main-scanning direction and a sub-scanning direction incident onto a mirror sinusoidally driven.                [Patent Document 1] JP-A-2001-281583        [Patent Document 2] JP-A-H11-84291        [Patent Document 3] JP-A-2006-178346        [Patent Document 4] JP-A-2006-227044        
The laser projection device described in Patent Document 3 uses a MEMS mirror that deflects laser light in two directions, i.e., the horizontal scanning direction and the vertical scanning direction in order to perform two-dimensional scanning. On the MEMS mirror, laser light converged is made incident in both the horizontal scanning direction and the vertical scanning direction, which does not contribute to the downsizing of the device due to no difference or a small difference, if any, in the degree of convergence of this laser light between the two directions. Moreover, the size of a projection optical system (approximately 40 times the mirror size) is large, in which point it is also hard to say that downsizing is achieved. Therefore, the configuration is not satisfactory to achieve a projection optical system compact in size and also capable of correcting arcsine characteristics and distortion. In any case, since light incident on the MEMS mirror is convergent light both in the horizontal scanning direction and the vertical scanning direction, it is required to adjust the position of the MEMS mirror in the both scanning directions. Moreover, since a projection optical system having a negative optical power is also used for the vertical scanning direction, there also arises a problem of difficulty in achieving constant speed performance in the vertical scanning direction.
In the laser projection device described in Patent Document 4, in order to achieve arcsine characteristics (constant speed scanning performance on a projection surface), laser light convergent in the horizontal scanning direction is made incident on the MEMS mirror. However, this laser projection device is configured to perform one-dimensional deflection and scanning, while not considering two-dimensional distortion. Moreover, the projection optical system is formed with one negative lens, and thus cannot correct two-dimensional distortion in principle.